This invention relates generally to the field of nuclear power plants, and in particular, it concerns a system for the automatic movement of fuel assemblies within a nuclear power plant during the refueling of the nuclear reactor.
Nuclear power plants which employ light water reactors require periodic outages for refueling of the reactor. New fuel assemblies are delivered to the plant and are temporarily stored in a fuel storage building, along with used fuel assemblies which may have been previously removed from the reactor. During a refueling outage, a portion of the fuel assemblies in the reactor are moved from the reactor to the fuel storage building. A second portion of the fuel assemblies are moved from one core support location in the reactor to another core support location in the reactor. A third portion of the fuel assemblies are moved from the reactor into fuel assembly storage locations in the fuel storage building. New fuel assemblies are moved from the fuel storage building into the reactor to replace those fuel assemblies which were removed. These movements are done in accordance with a detailed sequence plan so that each fuel assembly is placed in a specific location in accordance with an overall refueling plan prepared by the reactor core designer.
Refueling activities are often on the critical path for returning the nuclear plant to power operation, therefore the speed of these operations is an important economic consideration for the power plant owner. Furthermore, the plant equipment and fuel assemblies are expensive and care must be taken not to cause damage due to improper handling of the fuel assemblies or fuel transfer equipment. The precision of these operations is also important since the safe and economical operation of the reactor core depends upon each fuel assembly being in its proper location. Current refueling systems rely to a great extent upon the skill and discipline of the refueling crew, since human beings operate the fuel transfer equipment. There have been some efforts to automate portions of the refueling operations, for example, U.S. Pat. No. 4,427,623, issued to N. C. Howard, et al, teaches an apparatus and method for the automatic movement of fuel assemblies between locations in the reactor containment building. However, this patent does not address the movement of fuel assemblies within the fuel storage building or between the fuel storage building and the reactor containment building. Furthermore, existing systems have limited flexibility for dealing with unforseen changes in the refueling plan or sequence plan, such as may be necessitated by the discovery of a leaking or damaged fuel assembly. These plans are generated prior to the plant outage, and any revision to the plans requires the fuel shuffling operations to be placed on hold. In general, nuclear power plant refueling operations today are primarily controlled by human beings, with all of the schedular, safety, and economic limitations inherently associated with manual operations.